Character assassination is the process of harming a person's reputation enough to cause rejection of that person from their community. The phrase "time heals all wounds" doesn’t apply, which is why it's called an assassination.
Humans, by nature, work and live in groups and have criteria for acceptance and rejection. It's a mechanism for justice, and a way to enforce standards of behavior in group members. The threat of rejection is the enforcement muscle.
Humans, by nature, also have the ability to rationalize and 'toe the line'. One definition of power is be able to get your community to think the way you want them to think. The threat of force (loss of job, for example) is very powerful in getting people to see things your way.
Character assassination is the predatory use of this power to cause a person to be rejected from his/her community. It is characterized by; a moral rationalization of the community to reject the person based on character (or 'rumors' of bad behavior), not allowing the accused a voice in the discussions (or even to hear the charges, if possible), and the abuse of power to further this goal.
Structurally, a characterassassination requires for its commission three parties, the characterassassin or agent, the public whose estimation is to be altered or audience, and the person targeted or victim.
The study of characterassassination is a study of the methods and the psychology of the agent; it is a study of the credibility of the agent's slanders to the audience - that is, an attitude change question; and it is the study of the responses and the adaptation of the victim.
Characterassassination is a process of attitude change whose dependent variable is reputation and which is governed by three independent variables, viz.
Characterassassination is an intentional attempt to influence the portrayal or reputation of a particular person, whether living or a historical personage, in such a way as to cause others to develop an extremely negative, unethical or unappealing perception of him or her.
In practice, characterassassination usually consists of the spreading of rumors and deliberate misinformation on topics relating to one's morals, integrity, and reputation.
In politics, perhaps the most common form of characterassassination is the spread of allegations that a candidate is a liar.